Maryland's Invasive and Exotic Species

Are Zebra Mussels in the Chesapeake Bay?

Yes, zebra mussels occur in various parts of the Chesapeake Bay watershed in Pennsylvania and New York and more recently in a small part of Maryland’s waters.

In the summer of 2000, zebra mussel populations were discovered in Eaton Brook Reservoir and Canadarago Lake, in the upper Susquehanna River watershed of New York. In June 2004, zebra mussels were collected in Goodyear Lake, the first major impoundment of the Susquehanna River, near Cooperstown, New York. Scientists from the State University of New York at Oneonta later confirmed that the downstream movement of larval zebra mussels from Canadarago led to successful colonization of the Upper Susquehanna River.

In 2002, a population of zebra mussels was discovered in Millbrook Quarry, a popular recreational diving spot near Haymarket, Virginia. Although hydrologically isolated, the quarry is adjacent to Broad Run, a tributary to Lake Manassas and the Potomac River. The Virginia Department of Game and Inland Fisheries developed and implemented a plan that successfully eradicated this population with a chemical treatment in early 2006.

In 2008, zebra mussels were first reported in Maryland within the Conowingo Pool of the Susquehanna River. The following year, biologists with the Department of Natural Resources found 11 adult zebra mussels downstream of Conowingo Dam while surveying fish and native mussel communities. Since 2009, there have been regular findings of zebra mussels in the Susquehanna River immediately downstream of the dam. More recently, DNR has observed zebra mussels attached to the anchors of the navigational and hazard buoys that are placed throughout the the Upper Chesapeake Bay annually. In 2014, a near fifty fold increase in the number of mussels attached and anchors colonized was found. Several municipalities in the area have also began reporting clusters of zebra mussels attached to their water supply intakes or larva entering their intake pipes.

While zebra mussels are currently restricted to a small part of Maryland, their numbers are increasing and the current risk of dispersal to other water bodies is high. Fouling of intake pipes for municipal water supplies and power plants is a major concern because it can cost millions of dollars in upgrades, repair, and treatment per year. They also pose a serious threat to the integrity of our aquatic ecosystems and infrastructure. For example, dense zebra mussel aggregations are thought to increase the likelihood of harmful algal (Microcystin) blooms in the Great Lakes. In what could be considered a realistic example of their potential impacts to the Upper Chesapeake Bay, zebra mussels altered dissolved oxygen levels, aquatic plants, plankton, forage fish, and game fish communities in the tidal Hudson River following their initial population explosion. After 20 years, zebra mussel densities have decreased, but they remain a ubiquitous part of the estuaries’ aquatic life. This new “normal” in the river’s ecology cannot be reversed.

The material below explains the possible effects and what people can do to avoid spreading this invasive species to uninfested areas. The U.S Geological Survey and 100th Meridian initiative are also valuable sources of information.